The early morning air in Delhi is nothing short of poisonous. Apart from the two spikes in air pollution during rush hour traffic, Delhi’s third spike is after midnight due to the heavy movement of commercial vehicles with poor emission standards.

The pollution levels in Delhi are extremely high between 2 am and 4 am. This coincides with the time frame during which commercial vehicles, particularly trucks, are allowed to ply. “There can be no clearer indication of the correlation than this spike. The colder temperatures in Delhi at night lead to these pollutants being trapped and, hence, in the early morning, one can often observe smog-like conditions,” said Anumita Roychowdhury, Centre for Science and Environment (CSE).

Experts said that with most commercial vehicles using diesel — a fuel notified by WHO as a class I carcinogenic (the same category as tobacco) — this early morning smog is extremely dangerous. “Diesel vehicles emit higher levels of nitrous oxide and particulate matter than petrol vehicles,” said Roychowdhury.

Delhi is among the 13 cities in India that follows the Bharat Stage (BS) IV emission norms, while smaller cities implement BS III norms. The BS IV emission norm is equivalent to the Euro IV emission norms that Europe had discontinued in 2006. BS III is almost a decade older than global emission standards.

To put the threat posed by this laxity in the implementation of emission norms in perspective, one only needs to look at the sulphur content in diesel. In 2009, Euro V norms, which allowed a sulphur content of 10 parts per million (ppm), were introduced in Europe.

In comparison, Delhi’s BS IV emission standards have a sulphur content of 50 ppm while other vehicles following BS III norms are allowed a sulphur content of 350 ppm. Prolonged exposure to the emanating sulphur oxides can lead to respiratory diseases and even premature death, according to WHO.

What makes matters worse is that most of these trucks are not destined for Delhi. On December 6, 2001, the Supreme Court had ruled, “no heavy, medium or light goods vehicles will ply on inter-state routes by passing through New Delhi”.

Following the order, the Traffic Police had drawn up a list of four alternate routes that would allow the trucks to bypass Delhi —Ghaziabad to Punjab via Sonipat, Sonipat-Gurgaon-Rajasthan, Gurgaon-Faridabad-Uttar Pradesh and Faridabad-Noida-Ghaziabad.

But inadequate infrastructural improvements on these routes has ensured that the apex court’s decade-old order remains on paper, with no one agency willing to take responsibility for its implementation.